1. Field of the Invention
The present invention relates in general to a seat reclining mechanism, and more particularly to a seat reclining mechanism for adjusting the angular position of a seatback relative to a seat cushion by a planetary gear arrangement.
2. Description of the Prior Art
Hitherto, various types of seat reclining mechanism have been proposed for adjusting the angular position of a seatback relative to a seat cushion, which include a type of mechanism to adjust the angular position by a planetary gear arrangement. With this type of mechanism, the angular position of a seatback can be steplessly adjusted relative to a seat cushion.
For example, Japanese Utility Model First Provisional Publication 60-187645 discloses a seat reclining mechanism which employs a planetary gear arrangement. This seat reclining mechanism comprises a base plate, a pivotable arm, a rotatable shaft, two control gears, four planetary gears and a supporting plate. The base plate and the pivotable arm are pivotally interconnected by the rotatable shaft. The base plate and the pivotable arm have circular recesses respectively, which are generally opposed to each other. The base plate and the pivotable arm are respectively formed with ring gears at cylindrical surfaces defined by the circular recesses. The control gears are mounted on the rotatable shaft, and one of them is selectively fixed to the rotatable shaft so as to be rotatable therewith. The planetary gears are meshed with the control gears and with the ring gears surrounding the planetary gears. Each planetary gear has larger-diameter and smaller-diameter toothed portions. The supporting plate is rotatably mounted on the rotatable shaft. The supporting plate is generally disklike in shape and has four concave depressions by each of which the smaller-diameter toothed portion of the planetary gear is held in a predetermined revolution orbit around the control gears. However, the seat reclining mechanism has the following drawbacks.
The seat reclining mechanism has an unsatisfactory durability due to abrasion of the smaller-diameter toothed portion of the planetary gear and/or the supporting plate. It is necessary to apply a relatively large torque to rotate the rotatable shaft due to friction between the smaller-diameter toothed portion of the planetary gear and the supporting plate.